This application responds to RFA-HL-02-001 entitled "Transfusion Medicine/Hemostasis Clinical Research Network" and consists of four major sections: 1) descriptions of the proposed Transfusion Medicine/Hemostasis Core Clinical Center, investigator experience with clinical trials, the environment (DeGowin Blood Center, General Clinical Research Center, Hemostasis/Thrombosis Laboratory), and the plethora of patients with transfusion/hemostatic disorders available to participate in proposed clinical trials; 2) one short-term multicenter clinical trial entitled "Recombinant Activated Protein C and Plasma Exchange in the Treatment of Thrombotic Microangiopathies" which compares several clinical and laboratory outcomes of patients with thrombotic microangiopathies randomly assigned to either standard (therapeutic plasma exchange) or experimental (therapeutic plasma exchange plus activated protein C) therapy arms; 3) one long-term multicenter clinical trial entitled "Rituximab and Immunosuppressive Drugs in the Treatment of Acquired Autoantibodies Against Factor VIII" which compares outcomes of patients with acquired autoantibodies against clotting factor VIII randomly assigned to either standard immunosuppression (cyclophosphamide, vincristine, prednisone) or experimental (identical immunosuppression plus Rituximab anti-CD 20) therapy arms; and 4) an appendix containing data and letters of commitment from key individuals to document our abilities to fulfill all requirements of RFA-HL-02-001. Because of the expertise of the investigators, the excellence of the environment, the large number of potential study subjects and the quality of the experimental/ statistical design of the proposed clinical trials, it is likely that The University of Iowa Core Clinical Center will actively participate and make meaningful contributions to the NHLBI Transfusion Medicine/Hemostasis Clinical Research Network.